Splunk® Data Stream Processor

Function Reference

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Time Series Decomposition (STL)

The Time Series Decomposition (STL) algorithm automatically decomposes time series data streams into trend, seasonal, and remainder components in real time, enabling use cases like demand forecasting and anomaly detection to identify outliers.

Time Series Decomposition (STL) implements the streaming version of proven STL (seasonal and trend decomposition using Loess) approaches. The model input is a single stream of numeric time series values. For each raw datapoint observed ingested in input, the model predicts three values corresponding to trend, seasonality, and remainder as output.

This version of the Time Series Decomposition (STL) algorithm only separates a single seasonality from the input time series. It requires the user to specify an estimated periodicity of the observed seasonality (e.g., daily, weekly, or monthly).

Function Input/Output Schema

Function Input
This function takes in collections of records with schema R.
Function Output
This function outputs collections of records with schema S.


The required fields are in bold.

| stl value="input" seasonality=100;

Required arguments

Syntax: integer
Description: Seasonality sets the periodicity in the data.

Syntax: long
Description: Timestamp that comes with the value.
Syntax: double
Description: Use Time Series Decomposition (STL) on this value.

Optional arguments

Syntax: integer
Description: Set samplingRate in cases where timestamps are at irregular intervals.
Example: 10


For each observed data point, Time Series Decomposition (STL) computes a trend, seasonality, and residual value. This function can be applied to numeric time-series data, such as metrics or KPIs, to monitor for sudden changes or outliers in any of the three time-series components.

It can be challenging to identify anomalies in time-series metrics with high seasonality. For example, users monitoring web traffic may want to flag abnormally high activity that indicates an unexpected surge, or low activity that indicates a server is down. Traditional anomaly detection approaches may erroneously flag seasonal effects as anomalous - such as quiet hours over the weekend, or high volume days mid-week.

To overcome these false alarms, the Time Series Decomposition (STL) function can be used to first separate the seasonality and trend from the residual numeric time series values. Then, an anomaly detection model like Adaptive Thresholding can be applied to the residual. This approach is proven to improve anomaly detection accuracy to identify outliers, rather than erroneously flagging noisy data.

SPL2 examples

The following example uses Time Series Decomposition (STL) on a test set:

| from splunk_firehose()
| eval json=cast(body, "string"),
       input=parse_double(ucast(map_get('json-map', "Bytes Sent"), "string", null)),
       key=ucast(map_get('json-map', "Source Address"), "string", null),
       time=ucast(map_get('json-map', "Start Time"), "string", null),
       timestamp=cast(div(cast(get("time"), "long"), 1000000), "long")
| stl samplingRate=10 value="input" seasonality=100; 
Last modified on 02 December, 2020
To Splunk JSON

This documentation applies to the following versions of Splunk® Data Stream Processor: 1.2.0

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